Crystal Structure of Piezoelectric Ferromagnetic Gallium Iron Oxide

Abstract

The crystal structure of Ga2—xFexO3, with 0.7≤x≤1.4, has been determined at 298°K by x-ray diffraction. Ga2—xFexO3 crystallizes in the orthorhombic system, space group Pc21n, with lattice constants a = 8.7512±0.0008, b = 9.3993±0.0003, c = 5.0806±0.0002 Å and eight formula weights in the unit cell. The complete scattering pattern was measured with PEXRAD to (sinθ)/λ≤1.02 Å−1. One gallium atom in the asymmetric unit is in a tetrahedral site, the other gallium and the two iron atoms are in octahedral sites. For x>1, the excess iron partly occupies the octahedral gallium site: the iron sites are to a smaller extent occupied by gallium. The gallium tetrahedron is very nearly regular, with Gatetr−0 = 1.846±0.005 Å. The gallium octahedron is irregular, with average Gaoct−0 = 2.026±0.004 Å; the iron octahedra are somewhat more irregular, with average Feoct−0 = 2.036±0.004 and 2.049±0.004 Å in the two crystallographically independent octahedra. The oxygen atoms pack in pseudohexagonal layers with a double-hexagonal close-packed repeat. The absolute configuration has been determined by the anomalous scattering: the positive sense of the polar b-axis is essentially parallel to an 0→Gatetr bond. The thermal vibrations in the crystal are isotropic, with a characteristic temperature Θ of 534°K. The magnetic spin structure has been deduced, and an atomic mechanism postulated for the piezoelectric effect, in terms of the crystal structure.